Recently, development in compact and large-capacity optical disc devices is advancing to handle high definition still images and moving images and the like in the field of recording or reproducing information signals using an optical disc as an information recording medium.
The optical disc device is equipped with an optical pickup for forming a beam spot on an information recording surface of the optical disc. In the optical pickup, the light beam emitted from the light source is influenced by spherical aberration when passing through a transparent protective substrate layer which protects the information recording layer of the optical disc.
Japanese Unexamined Patent Publication No. 2004-77705 discloses a device in which a lens group for spherical aberration correction is arranged, a variable clearance is formed between surfaces of a pair of successive lens elements in the lens group, and a clearance interval is varied through a mechanical method to alleviate the influence of spherical aberration.
FIG. 8A and FIG. 8B are views showing in frame format a configuration of an example in which the conventional lens drive device of patent document 1 is applied to an optical pickup, where FIG. 8A is a plan view of the optical pickup, and FIG. 8B is a side view of the optical pickup.
In the figures, 114 denotes an optical disc, 101 denotes a laser diode serving as a light source, 102 denotes a collimator lens, 103 denotes a beam splitter, 104 denotes a rising mirror, 105 denotes an objective lens, 106 denotes a detection lens, and 107 denotes a photodetector including photoelectric conversion element etc.
When performing recordation/reproduction on the optical disc 114, the light beam emitted from the laser diode 101 is passed through the beam splitter 103 and the collimator lens 102, deflected towards the optical disc 114 by the rising mirror 104, and collected on a recording surface of the optical disc 114 as an optical spot by the objective lens 105. The light beam reflected at the surface of the optical disc 114 is passed through the objective lens 105, deflected by the rising mirror 104, passed through the collimator lens 102, deflected by the beam splitter 103, and collected on a light receiving surface of the photodetector 107 by the detection lens 106.
The collimator lens 102 is a lens for correcting diffusion and convergence of the light beam by moving the position in the optical axis direction. The collimator lens 102 is held by a lens holder 108, and the lens holder 108 is supported by a pair of shafts including a guide shaft 109 and a slidable shaft 110. The guide shaft 109 and the slidable shaft 110 are fixed to a shaft holding member 113. The guide shaft 109 and the slidable shaft 110 are arranged so that the extending direction of the respective shaft becomes parallel to the optical axis of the collimator lens 102.
The lens holder 108 is slidably engaged with the guide shaft 109 and the slidable shaft 110. That is, the collimator lens 102 can move in the optical axis direction when the lens holder 108 slidably moves along the guide shaft 109 and the slidable shaft 110. A drive mechanism (not shown) configured by a gear, a stepping motor, or the like is arranged as a mechanism for moving the lens holder 108. The lens holder 108 moves in the optical axis direction when the slidable shaft 110 slidably moves in a thrust direction in response to the drive power from the drive mechanism.